This weekend, when speakers at Earth Day gatherings across the country hearken back to the first celebration in 1970, they'll recall great victories: above all, cleaner air and cleaner water for Americans.

But for 20 years now, global warming has been the most important environmental issue -- arguably the most important issue the planet has ever faced. And there we can boast an unblemished bipartisan record of accomplishing absolutely nothing.

To mark Earth Day this year, Sens. John Kerry (D-Mass.), Lindsey Graham (R-S.C.) and Joseph Lieberman (I-Conn.) were supposed to introduce their long-awaited rewrite of the House's climate legislation. Now that's been delayed for at least a few days, which is probably just as well, since, as Graham points out, it's no longer really an environmental bill.

"I'm all for protecting the planet, but this is about energy independence," Graham said last week. The bill's emission reductions are weakened by offsets and loopholes -- and to win support for even those concessions, it offers the fossil-fuel industries a glittering collection of door prizes. President Obama himself has already offered the first of these bent-knee offerings: a return to the full-on offshore drilling that was one of the targets of the first Earth Day. Now a new generation will have a chance to experience its own Santa Barbara oil spill, with its iconic oil-soaked birds.

Worse, the bill might specifically remove the strongest tool the environmentalists won in the wake of Earth Day 1: the Environmental Protection Agency's right to use the Clean Air Act to bring the fossil fuel industries to heel. Enforcement may be preempted under the new law. Even the right of states to pioneer new legislation, such as California's landmark global warming bill, apparently could disappear with the new legislation.

So when the media and the president hail it as a "landmark," understand the shifting ground it actually defines: The environmental idea is too weak right now to win passage of a tough bill to deal with our greatest problem. It will settle for half measures, when it gets the chance to settle for anything at all.

That weakness has many sources, including the corrosive power of money in politics (and human beings have never found a greater source of money than fossil fuels). But at least part of the problem lies within environmentalism, which no longer does enough real organizing to build the pressure that could result in real change. Many of our largest environmental groups are still running on the momentum they built up in the early 1970s -- if you don't believe me, look at the average age of their members. They are still fighting the noble fight, but now they're mostly doing it from inside the Beltway. And their lobbying has far less impact than it should, because the politicians they seek to influence know they lack the punch to reward or punish.

I remember interviewing Pete McCloskey, the California House member recruited by Gaylord Nelson to be the Republican sponsor of the original Earth Day. The gatherings themselves, he recalled, came as a revelation -- not celebrity-driven or corporate-sponsored but a pure outpouring of anger and hope, with people smashing donated cars with sledgehammers and planting flower gardens in city squares.

But just as important was what happened next: "About two weeks after Earth Day," McCloskey said, "there was an article on the sixth or seventh page of the Washington Star -- some of the Earth Day kids had labeled 12 members of Congress the Dirty Dozen and vowed to defeat them. Nobody paid much attention. On the first Wednesday in June, though, everyone in Washington opened the paper to find that the two Democrats on that list -- one a powerful committee chairman, the other a senior member of the House Judiciary Committee -- had lost primary fights by fewer than a thousand votes. Within 24 hours, seven of the 10 Republicans on the list had come to me, even though I was despised, being against the war and all. 'What's this about water pollution, about air pollution? What can you tell us?' " For the next few sessions, anything tinged green passed Congress with ease: the Clean Air Act, the Clean Water Act, the Endangered Species Act.

Organizing is not impossible, even today. In some ways, in fact, it's easier. At 350.org, which argues for ambitious carbon reductions, we've managed to use the Web and social media to help build a real-world network -- last fall we organized 5,200 simultaneous rallies across the world, what Foreign Policy called the "largest-ever coordinated global rally of any kind." But it wasn't enough to carry the day at Copenhagen, though we did persuade 117 nations to sign on to our targets. So we'll be back at it on Oct. 10, with a Global Work Party in thousands of communities around the globe.

It's designed to send a pointed message to our political leaders: Get to work. But that same message applies to the environmental movement, too.

Bill McKibben is a scholar in residence at Middlebury College and author of "Eaarth: Making a Life on a Tough New Planet."